9/11 Physics from Non-Experts

GregoryUrich said:
This only effects the PE not the total mass. I still have 100,000 tons of steel.

One problem related to this is that the floor joists shouldn't be smoothed because they are the same on every floor. This introduces a maximum error for PE of around +5% and -5% at the top and bottom of the building respectively. I will correct for this in my next version.
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i beg to differ. BEG! :0
 
have you looked at the blueprints? 66th floor Greg, 66th floor! this is not unusual.
 
279,000 tons

R.Mackey said:
Yes, in that case, you do indeed deserve my profound apology. I was careless.

Their steel calculations are quite thorough. It appears, however, that they conclude the 500,000 short ton estimate for the total tower weight is accurate assuming the Towers were loaded to full live load. Thus even if we assume a service live load of only 25% design live load (which feels pessimistic), we lose only 1000 short tons per floor, suggesting the 500,000 short ton estimate is high by perhaps 110,000 short tons. This would give us an answer in the 390,000 short ton ballpark.

I've said before, I don't know whether the true weight was closer to 400,000 or 500,000 tons, but I'm still having a lot of trouble swallowing 250,000 tons.
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My result is 279,000 short tons. Please don't missquote me.

You are forgetting the basement and core.

Outside the core(design 100 psf): 31,000 x 75 psf x 110 = 127,875
Inside the core (design 50 psf): 5000 x 37.5 x 110 = 10,313
Basement (design 500 psf): 31,000 x 375 x 6 = 34,875

So we are talking about approx. 170,000 tons.
 
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I don't think you can reduce the basement load by 75%, not even under the most optimistic scenario. But I included the core.
 
R.Mackey said:
I don't think you can reduce the basement load by 75%, not even under the most optimistic scenario. But I included the core.
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My point was that if I use 100% design loads I need to add 170,000 tons which puts my estimate at 449,000 tons.
 
Not following you. I thought you said that 100% of the design (live?) loads came to 170,000 tons, which seems about correct.

But you should already have about 25% design loads already included, right? So wouldn't you only add about 127,500 tons?
 
the core and exterior structurer was consistent up to this point. we don't taper in a linear fashion. makes no sense.
 
hey, why take the opinion of a professional, the engineers sound like they know what they are doing.
 
R.Mackey said:
Not following you. I thought you said that 100% of the design (live?) loads came to 170,000 tons, which seems about correct.

But you should already have about 25% design loads already included, right? So wouldn't you only add about 127,500 tons?
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170,000 is 75% of design loads (see my calc above).
 
Greg, long story short I've built buildings. You haven't. Trust me, your're wrong.
 
GregoryUrich said:
170,000 is 75% of design loads (see my calc above).
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Ah, I see. Yes, you made no mistake there.

You're still 60,000 tons of superimposed dead load short, however, and we are relying on an assumption that the publicly accepted figures assume 100% design load, which is unproven.

In other words, all this proves is that your structural load is credible, and I believe I already said I agreed with that. It's the rest that doesn't makes sense.
 
3bodyproblem said:
the core and exterior structurer was consistent up to this point. we don't taper in a linear fashion. makes no sense.
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I think you are correct regarding the outside dimensions of the columns, but I don't see plate thickness anywhere in the diagram.

I wasn't suggesting that the outer dimensions taper but the plate thickness does. In fact the exterior columns have the same outer dimensions all the way up after the 7th floor.

What would make sense is starting with the strongest grade lowest in the building and varying the grade to retain a symetrical joint up until the weakest grade and then changing the plate thickness and starting over with the strongest grade.

If I remember correctly, they didn't use alot of different grades in the core.
 
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Gregory Urich

The mass of each tower is very interesting, but NOT crucial to the collapse.

Free fall in gravity is independent of the mass of each tower after all!

The fact that, as NIST clearly state, the Towers fell from aircraft impacts alone is more significant.

Did the perpetrators know this beforehand, or not?

The NIST Report makes sure that it adds that the fires were the problem...

But if NIST are only figuring this out now, is it possible that the US government could be so unaware of something the perpetrators had probably calculated twenty years ago; as we calculate it now, with hindsight.

Or did the perpetrators just get lucky?

It looks to me like the Towers COULD NOT survive aircraft impacts!

I would like to know why somebody would say otherwise...
 
Are you a bricklayer?

3bodyproblem said:
Greg, long story short I've built buildings. You haven't. Trust me, your're wrong.
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Then you should be able to confirm that, averaged over the total floor area, an actual load equal to 25% of design load is pretty normal. If not, I have to assume you are a bricklayer.
 
NIST actually provide some decent info on the office contents, although they don't provide weight. However good weight estimates can be obtained from load calculators used by commercial moving companies.

For the purposes of this little experiment, I have used the 3D model of the layout of the 96th floor of WTC1 as appears on page 95 of NISTNCSTAR1.

I count a total of 204 office cubicles. According to NIST these cubicles were fairly standard across the building, typically 8ft x 8ft, bordered on all four sides by panels, with a small opening.

Photos provided by NIST show at least one side in some cases reached to about shoulder height. Desks were typically wood of a typical large corner-orientated office design. The photos I've seen indicate these cubicles were generally pretty cluttered.

In addition, on the 96th floor I count 27 "small" enclosed offices (1.5 - 2x cubicle size). These appear to be enclosed by more substantial floor to ceiling internal walls.

I count 10 "medium" enclosed offices (3 - 4x cubicle size). And I count 4 "large" enclosed offices (6-8x cubicle size).

Now, for the cubicles, assuming all divides are an equal waist height (photos suggest some divisions were higher) and assuming the 8ft square figure with a 3ft opening in each cubicle, based on the layout of the floor I get a total of 3,852ft of dividing screens.

Anyone care to make a stab at how heavy these are? Just for clarity these do appear to be semi permanent rather than the light weight movable ones you also get in offices.

If we assume of height of about 1.2m (~4ft) and thickness of 3inches.

Now, what would these be made of? We've got a total volume here of 107m3.

If it's particle board, for example, we're talking 17 - 48 tonnes. If it's high density fibre board we're talking 53 - 155 tonnes.

Assuming the "cubicle - 200lbs" weight we were given is meant to be the divides, we're meant to believe these divides only weigh about 20 tonnes, and that for 25% more cubicles.

(If anyone does know what such divides are normally made of, it would be a help).

Using several commercial moving weight calculators and basic furnishing for one cubicle, I get typically around 400kg just for furniture. This doesn't include contents, computers, or anything like that. And I want to reiterate this is BASIC furnishings. Now my meagre basic home office files weigh in at 25kg, and I would estimate the average office (at least the ones I've ever been in) has at least 3 times as much, with a more paper-heavy job (accountant, for example) having as much as 10x as much paper work stored in their personal workspace. I think anything from 75 - 250kg worth of files per cubicle would be reasonable. Half way is 160kg. My computer (just monitor and case) weighs 30kg.

As you can see it begins to add up quickly. And I haven't addressed our 41 larger offices, which have heavier floor to ceiling internal walls (doors?), much more furniture and so on.

I look at the figures presented previously, and I'm highly skeptical.

I mean, 1,000 conference chairs weighing 20 tons? That's about 20kg a chair. Yet you claim this is excessively heavy "made of concrete". Now I doubt there'd be 1,000 conference chairs on every floor, but I'd guarantee you they weigh a LOT more than 20kg. My lame little swivel chair at home (horrible thing, by the way) weighs 10kg. I cannot physically pick up a decent conference chair on my own. I'd imagine they weight a good 50kg at least.

To illustrate my point, no account is made for stationary storage. When I was working at the Auckland offices of GlaxoSmithKline (about 100 staff) I helped with moving one of our several paper storage areas. Based on 80gsm photocopy paper, they had over half a tonne just of plain white copy paper (50 boxes of 5 reams), just in this one storage area. That's not including all of the other paper they had there, or the boxes of paper stored by photocopiers, or the other bulk storage areas (at least one, possibly three).

Now a couple of tonnes of white copy paper might not seem like much, but this is just one example of weights that haven't been factored in. What about kitchen facilities? Bathrooms? We received 20kg of mail a day, for a company with 100 employees. Multiply that by the 25,000 people who worked in each tower and you've got 5 tonnes of just MAIL.

How many ballpoint pens? How many staplers? How many tins of coffee and cans of soft drink? There's literally thousands of things here that have been totally ignored, and added together that amount to tonnes and tonnes of live weight.

-Gumboot
 
Apollo20 said:
But if NIST are only figuring this out now, is it possible that the US government could be so unaware of something the perpetrators had probably calculated twenty years ago; as we calculate it now, with hindsight.

Or did the perpetrators just get lucky?
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According to Osama Bin Laden (who, let's remember, is an engineer), he anticipated the upper sections collapsing but didn't expect the entire building to collapse.

I don't know how familiar he was with the construction of the towers.

-Gumboot
 
gumboot said:
According to Osama Bin Laden (who, let's remember, is an engineer), he anticipated the upper sections collapsing but didn't expect the entire building to collapse.

I don't know how familiar he was with the construction of the towers.

-Gumboot
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Perhaps someone can dig up the clip, but shortly after the first attempt (bomb in the basement, near the core), we actually told them how to do it--I'll paraphrase, but the engineer said "they thought damaging the core would do damage, but this building doesn't have a conventional core. Most of the building's weight isn't carried in the core, it's in the perimeter columns"
 
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